[Soil and Crop] Add manure carbon to soil carbon pools

[KFosterReed]

Is your feature request related to a problem? Please describe.

When manure is added to soil, it adds carbon in addition to the N and P that is already being added. Currently, RuFaS does not include representation of any manure carbon to the soil carbon pools. This reduces the accuracy of the changes in soil carbon stocks over time in fields that have manure applied to the soil.

Describe the solution you'd like

I believe this can be accomplished by the following steps:

1. Estimate the amount of manure carbon applied.
2. Create a Manure Carbon Residue pool in each soil layer that is analagous to the plant_residue pool.
3. Add manure carbon to the Manure Carbon Residue pool at each manure application
4. Partition the Manure Carbon Residue in each layer into the soil metabolic carbon and soil structural carbon according to the ratio of lignin : nitrogen in the manure.

The above is described in more detail in the design doc initiated by Carbon Yield.

Alternative Solutions

• One alterntive solution to the amount of manure carbon applied is to make the amount of manure carbon applied be an input analagous to the current manure N and P application amounts. This option would be a large increase on the input burden for the user and is not connected to how manure application amounts and rates are applied.

Target Deadline

I think a target deadline July 31 is reasonable